1. Field of the Invention
The present invention relates to the generation of an internal supply voltage on integrated circuits; and more particularly to internal supply voltages having a lower potential than power supply potentials provided to the integrated circuit, and which consume very little stand-by power.
2. Description of Related Art
In the design of integrated circuits, a need often arises to provide a supply voltage on the integrated circuit which is lower than the voltage supplied by an external power supply. For example, in the design of flash memory devices, it is typical to provide an external supply voltage at about 5 volts, and at times, at about 12 volts. A number of other supply voltage levels are required for the complex procedures involved in a programming and erasing and reading the flash memory cells. The problems associated with various supply voltages in flash memory devices can be understood, for example, with reference to U.S. Pat. No. 5,295,113; entitled FLASH MEMORY SOURCE INHIBIT GENERATOR, invented by Dix, et al.
A circuit that supplies a supply voltage in an integrated circuit must be capable of sustaining substantial on demand current, in order to maintain the voltage potential at its output under varying load conditions. Prior art designs for generating internal supply voltages of this type, therefore have been relatively high power consumers. For example, in the Dix, et al. patent cited above, a low voltage supply circuit is described which is used for the so-called source inhibit function in a flash memory integrated circuit having the architecture described in Dix, et al. Although the supply circuits of Dix, et al. operate to provide a relatively stable internal supply voltage, they suffer the disadvantage that they consume substantial current even in the stand-by mode.
As the design of integrated circuits has evolved toward uses in which low current stand-by modes are important, a need has arisen to provide internal supply voltages with much less stand-by current consumption than has been available in the prior art.